ANATOMY OF THE CHEST WALL & PLEURA
The physiology of respiration and the anatomy of the chest wall are tightly linked. The chest wall is an airtight, expandable, cone-shaped cage. Normal ventilation occurs when expansion of the rib cage and simultaneous diaphragmatic excursion create negative intrathoracic pressure, allowing inward flow of air.
The function of the chest wall is made possible by its segmentally arranged anatomy. The ventral wall of the bony thorax extends from the suprasternal notch to the xiphoid, approximately 18 cm in the adult. It is formed by the manubrium, sternum, and xiphoid process. The remainder of the anterior wall and the lateral walls are formed by 12 ribs. The first seven pairs of ribs articulate directly with the sternum, the next three pairs connect to the lower border of the preceding rib, and the last two terminate in the wall of the abdomen. The sides of the chest wall consist of the upper 10 ribs, which slope obliquely downward from their posterior attachments. The posterior chest wall is formed by the twelve thoracic vertebrae, their transverse processes, and the 12 ribs (Figure 18–1). The upper ventral portion of the thoracic cage is covered by the clavicle and the subclavian vessels. Laterally, it is covered by the shoulder girdle and axillary nerves and vessels; dorsally, it is covered in part by the scapula.
The thorax, showing rib cage, pleura, and lung fields.
The superior aperture of the thorax (also called either the thoracic inlet or the thoracic outlet) is a downwardly slanted 5- to 10-cm kidney-shaped opening bounded by the first costal cartilages and ribs laterally, the manubrium anteriorly, and the body of the first thoracic vertebra posteriorly. The inferior aperture of the thorax is bounded by the twelfth vertebra and ribs posteriorly and the cartilages of the seventh to tenth ribs and the xiphisternal joint anteriorly. It is much wider than the superior aperture and is occupied by the diaphragm.
The blood supply and innervation of the chest wall are via the intercostal vessels and nerves (Figures 18–2 and 18–3). The upper thorax also receives vessels and nerves from the cervical and axillary regions. The underside of the sternum’s blood supply derives from the internal thoracic artery branches, which anastomose with the intercostal vessels along the lateral aspect of the chest wall.
Transverse section of thorax.
Intercostal muscles, vessels, and nerves.
The entirety of the thoracic cavity is lined by a pleural membrane. The parietal pleura is the innermost lining of the chest wall and is divided into four ...